1. Field of the Invention
The present invention generally relates to an optical proximity correction, and more particularly to an optical proximity correction method for modifying the polygon feature pattern with inner corner.
2. Description of the Prior Art
The minimum feature sizes of integrated circuits (ICs) have been shrunk for years. This feature size reduction, various process limitations have made IC fabrication more difficult. One area of fabrication technology in which such limitations have appeared is photolithography.
An important component of photolithographic apparatus is a xe2x80x9creticlexe2x80x9d which includes a pattern corresponding to features at one layer in an IC design. Such reticle typically includes a transparent glass plate covered with a patterned light blocking material such as chromium.
For advance SOC (system on chip), the complexity of design and the file size of mask tooling both dramatically increased. For example, a 50 GB (giga bytes) file size, it may take two days for mask writing. Therefore, how to reduce the file size is an important issue. The traditional OPC (optical proximity correction) methodology corrects the inner corner pattern by adding extra serifs. For a single inner corner, the number of data points can be expanded from one to five. Overall, this approach would increase the output file size and dramatically increase the mask writing time since the serif require adding extra data points. Thus, the data points of the file are increased and the writing speed is slow down.
FIGS. 1A to 3C show the conventional OPC (optical proximity correction) using inner serif for L-, T-, and cross-shaped feature patterns. Extra data points and mask writing units are required to define these OPC patterns. Small mask writing units causes a large file size, a complex and slower mask writing procedure.
FIG. 1A to FIG. 1C shown a reticle corresponding to an integrated circuit (IC) pattern. FIG. 1A shows an un-corrected L-shaped feature pattern 10. To avoid the L-shaped feature pattern with a corner, there is a method to modify the un-corrected L-shaped pattern 10 with an OPC method such as serif method to form a corrected L-shaped feature pattern 10a which has an inner corner 14 as shown in FIG. 1B. Therefore, the extra data points and the file size are also increased after correction steps. The un-corrected L-shaped feature pattern 10 has only one data point 12A, however, the corrected L-shaped feature pattern 10a has four extra data points, 12B, 12C, 12D, and 12E. Therefore, the computer data-processing capacity and file size are increased that according to increase of data points. Referring to FIG. 1C, the corrected feature pattern 10a is divided into five rectangular feature patterns 16a through 16e, such that increase two extra mask units after the mask dividing step.
Then, referring to FIG. 2A shown the uncorrected T-shaped feature pattern 20 with two data points 22A and 22B. The correcting steps as the FIG. 1A to FIG. 1C, a corrected T-shaped feature pattern 20a with two inner corners 24A and 24B are formed after serif correction method as shown in FIG. 2B and has eight extra data points 22C through 22J. In the FIG. 2C, there are seven extra mask units 26a through 26h after a mask-dividing step. Next, referring to FIG. 3A that shown the un-corrected crossed-shaped feature pattern 30 with four data points 32A through 32D. As the above-mentioned, after serif correction method, the corrected crossed-shaped feature pattern 30a with four inner corners 34a through 34d and has sixteen extra data points 32E through 32T, which are increased after OPC method. Therefore, the output file size is increased and the mask writing time is dramatically increased since the serif requires adding extra data points.
Next, the FIG. 4 is schematic vertical views showing a contour image of the un-corrected crossed-shaped feature pattern 30. The scope of the solid line is an original un-corrected crossed-shaped feature pattern 30, after exposure steps, the scope of dotted line is a simulation area image 40 is smaller than the original un-corrected crossed-shaped feature pattern 30. But the simulation area images have four corners 42a, 42b, 42c, and 42d, and further the corner still causes the pattern inspection issue. Furthermore, in order to solve the corner issue, the conventional technique is utilized a serif method to modify the conventional crossed-shape feature pattern 30. According to FIG. 3B, after exposure step, the simulation area image 40a is approach to the original feature pattern 30a with using serif method as shown in FIG. 5. In the FIG. 5, even though the simulation area image 40a is approach to the original feature pattern 30a, but the simulation area image 40a has corners and still causes the file size increased, loading mask time, and mask writing time are increased.
In accordance with the present invention, a method is provided to correct the feature pattern with inner corner fidelity by an optical proximity correction (OPC) method, the improved method substantially reduces the OPC output file size, improves the mask writing with a few rectangular-shaped writing units or trapeze-shaped writing units for regular mask writing, and save the mask inspection time.
It is an object of this present invention to provide an improved OPC (optical proximity correction) method without adding extra serifs to obtain a high-resolution pattern mask.
It is another object of this present invention to provide an effectively OPC to reduce the OPC output file size.
It is still another object of this present invention to provide an OPC method to correct the polygon feature pattern and perform the plurality of the mask writing with a few rectangular-shaped writing units or trapeze-shaped writing units for regular mask writing to improve the mask writing time.
It is a further object of this present invention to provide a method to improve the mask uniformity and feature pattern inspection.
In one embodiment, the approach of the present invention uses a pattern section without adding extra serif to correct the polygon feature pattern. Correcting the polygon feature pattern with at least one inner corner that can achieve effectively OPC (optical proximity correction) without adding extra data points and mask writing units. Therefore, the present invention can instead of four as the conventional serif and achieve the effectively OPC. In addition, the mask writing time is also improved since the original feature pattern is divided into a few rectangular-shaped mask writing units or trapeze-shaped mask writing units for regular mask writing units, and the inner corner is/are not in the middle of each of the divided mask writing unit (rectangular mask writing units or trapeze mask writing units). The feature pattern inspection is also simplified and easier to calibration since a simple geometry other than complex serif is used.